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I hear some version of this every week.
"My curls used to be so much tighter."
"My hair was straight my whole life, then went curly after I had my first child," and on the flip side, "After I had kids, my curls disappeared."
"My curl pattern completely changed after I turned 40."
The good news is that none of this is completely random. Curl changes fall into three distinct categories. Some of these changes are permanent, but many are completely temporary. And a significant number are actually damage being mistaken for something else entirely.
Let me break it down.
Your curl pattern is determined in the hair follicle, not in the visible length of hair growing out of your head. The shaft you have the deepest relationship with is a non-living tissue. The follicle underneath your scalp is the living organ producing it, and what comes out is shaped by the follicle's geometry. The curvature, the asymmetry of the bulb, and the way cortical cells are distributed inside the hair shaft determine your unique curl or wave pattern.
Hair is stabilized by three types of chemical bonds, and understanding them explains almost every curl change you will ever experience.
Hydrogen bonds are the most abundant and the weakest. Water breaks them easily and they reform when hair dries. This is why you curls reshape every wash day, why humidity changes your frizz level, and why a blowout lasts until you get caught in the rain (there's no hiding those curls).
Disulfide bonds are the structural backbone of your hair's shape. They are much stronger and require significant chemical intervention to break and reform. These are what perms and chemical relaxers target, which is why those processes produce more lasting results in the treated length of the hair.
Ionic bonds sit between the two in terms of strength. They are pH-sensitive rather than water sensitive, which is why hard water, mineral build-up, and certain shampoos can affect how your hair feels and behaves when it is dry.
Your curl pattern is largely inherited. If your mother had tight coils, there is a reason yours look similar. But genetics is more of a starting point than a fixed destination. Hormones, age, and external factors can shift how your follicles express that baseline over time. This is why your curls at 40 can look genuinely different from your curls at 20 even though your DNA has not changed.
When the follicle itself changes, the new hair growing out of it is different. This is real and lasting curl pattern change that shows up at the roots before you notice it in the rest of your hair.
Puberty is the clearest example most people can relate to. A lot of us had perfectly straight hair as kids and then somewhere around middle school noticed that the hair coming in at the roots looked completely different. The hormonal changes of puberty genuinely alter how your scalp follicles behave and the hair that grows out of them afterward can be thicker, wavier, or curlier than our younger-selves' hair.
Pregnancy is one of the most common reasons people tell me their curls changed; either their kids "took" their curls or "gave" them curls. There is a more scientific explanation for this. During pregnancy, high estrogen keeps more of your hairs in the growth pahase, which is why hair tends to feel thicker. After delivery, that estrogen drops fast and a large number of hairs shift into the shedding phase all at once. The new growth coming in to replace it is shorter and finer than the hair around it, and that mix of shedding nd new growth can make your curl pattern look very different. For most people, it settles out within a year. Lasting changes do happen, but they are less common than the temporary chaos of the postpartum period makes them feel.
Menopause brings its own version of hormonal upheaval, and your hair usually has something to say about it. As estrogen declines and androgens become relatively more dominant, the follicles start producing finer, thinner fibers. Density can decrease, texture can change, and the curls that felt reliable for decades can start behaving differently. Unlike the postpartum experience, which tends to hit fast and hard, this one is more of a slow reveal that unfolds gradually across the perimenopausal years, which can make it harder to notice until it is well underway.
Ageing gets less dramatic press than menopause but has an equally real impact on the texture of our hair. Over the decades, some follicles gradually start producing finer, thinner fibers and curls that were once dense and defined can become looser and harder to predict. But ageing also brings gray hair, which can change in a different way. When melanin production slows down, it changes the internal structure of the hair fiber itself, and the cuticle layer shifts in ways that make gray strands stiffer, coarser, and wirier than the pigmented hair that came before. Add in declining sebum production and those gray strands get drier on top of everything else. So ageing can genuinely pull curl pattern in two directions at once, making sure you stay on your toes. Some strands can become finer and looser while others come in coarser and kinkier.
Hormonal imbalances and medicationscan also change what grows out of your follicles, though the signs tend to be different from a typical curl pattern shift. Thyroid dysfunction, for example, usually shows up as coarser, drier, more brittle hair across the board rather than a tidy change in curl shape. Androgenic hormones can affect density and fiber caliber in ways that gradually loosen or alter an existing curl pattern. Some medications,like certain antiepileptics, retinoids, and chemotherapy drugs (hello, chemo curl!), have well-documented effects on hair texture that typically resolve after treatment changes, though how long that takes varies considerably. When it comes to the chemo curl, I have heard anecdotally that for some, the curls have persisted for years, while others say the new texture faded away more quickly.
This category covers the vast majority of day to day curl variation and it is almost entirely driven by the hydrogen and ionic bonds.
When your hair is wet, hydrogen bonds are broken and the strand becomes temporally flexible. As it dries, those bonds reform around whatever shape the hair is in at that moment. This is why styling technique matters so much; you are literally setting the bonds while they are open and protecting them while they close. For a more in-depth look into this, read Why Your Curls Look Defined Wet, But Frizzy When They Dry.
Humidity disrupts this process after the fact. Humid air introduces water molecules that can break and reform hydrogen bonds in the dried hair, shifting curl shape and amplifying frizz, particularly in porous hair where the cuticle is already more open. The curl pattern hasn't fundamentally changed, the bonds are just resetting in response to the environment.
Hard water minerals create different problems. Calcium and magnesium (or in my well-water case, iron) deposit on and inside the hair shaft. This can stiffen the strands, roughen the surface, and make it harder for the ionic bonds to form correctly over time. After a while, the curls will be less defined and feel drier even with a consistent routine. A clarifying wash removes the mineral build-up and the hair typically responds positively right away.
Product build-up works the same way. When layers of oils, conditioners and styling products accumulate on the hair shaft, they create a barrier. Hydration sits on the surface rather than absorbing in. Curls feel coated and heavy and lose their ability to clump properly. The follicle and the hair shaft haven't changed intrinsically, but the surface is blocked from forming the necessary bonds. Read The Science of Curl Clumping for a little more on these curl-clumping bonds.
All of these are reversible and the most manageable category of curl change. They are also commonly mischaracterized as being permanent curl changes.
This one falls in between a permanent change and a temporary change. But is still totally in your control. Damage to your curls doesn't affect hair at the follicle, but it also is not simply a temporary bond shift that resets at the next wash.
Repeated heat styling can denature the proteins in the cortex of the hair strand and weaken your curl pattern. This can also roughen the cuticle and weaken the disulfide bond structure enough that curls appear permanently looser, frizzier, and less coherent. The occasional blowout or flat iron session is mostly a temporary hydrogen bond shift that won't cause irreparable harm, but months of regular high-heat styling on the same sections is a different situation.
UV exposure oxidizes proteins and lipids in the shaft and degrades the cuticle. This is one reason the ends of longer hair can be rougher than the hair toward the roots; it has had many extra years of sun exposure.
Bleaching and chemical processing break disulfide bonds as part of how they work. Bleach in particular also damages the protein matrix of the cortex and cannot be undone in the treated length.
Hygral fatigue, which is the stress caused by repeated swelling when wet and contracting dry, can contribute to fiber fatigue and breakage over time, particularly with harsh washing routines or excessive wet manipulation, like sleeping on wet hair.
Curls that are dull, split, or breaking alongside the pattern change are showing some sort of damage. Curls that look looser or frizzier, primarily at the ends, mid -lengths, or the outer layer, while the roots feel healthy are almost certainly showing damage rather than a new follicle shift. Physical damage to the hair shaft is cumulative and doesn’t repair itself if the same damaging tactics are continued. While the only permanent resolution is cleaning up your ways, growing the hair out, and cutting the damaged length of hair off, you can introduce conditioners with curl enhancing proteins to soften the effects of damage.
This is the question that cuts through most of the confusion.
Change appearing at the roots or in new growth that behaves differently from the older lengths points to a follicle-level cause that may be more of a structural change and longer lasting: hormones, ageing, medication, or a health change affecting the biology of what the follicle produces. If your roots are curlier, wavier, finer, or coarser than they used to be, something upstream has shifted.
Change appearing at the mid-lengths and ends, while the roots still look and behave as expected, points to environmental exposure, styling, or damage affecting the existing shaft. The follicle is still producing the same hair, but what is coming out is being altered after it gets there.
Change appearing everywhere at once, with no clear distinction between roots and ends, can indicate either a systemic change that happened some time ago and has since grown out evenly, or a routine and environmental issue affecting the whole length simultaneously.
When texture change is accompanied by significant shedding, scalp symptoms, or other physical changes, a conversation with a medical professional is worth having. Some of the follicle-level changes in the permanent category are associated with health conditions that benefit from earlier rather than later intervention.
You can't change your genetics. You can't prevent ageing. You can't instantly reverse damage in the length of the hair.
What you can control is the foundation that determines how well your curls form and hold up over time.
Clean hair absorbs hydration and styling products better than hair with build-up. Using the right shampoo for your scalp and hair type removes what is sitting on your strands so everything applied afterward can do its job. If your curls have felt increasingly dull, heavy, or dry despite a consistent routine, this is where to start before changing anything else. You'd be surprised how many issues can be resolved by removing build-up.
Conditioned hair has more flexibility and resilience. The right conditioner for your curl typeprovides the slip and hydration that allow curls to clump together in the shower, which is where definition starts.
Supported curls have internal structure. Leave-in products applied to wet hair give indvidual strands the protein or moisture they need to group together instead of separating.
Sealed curls hold. A gel creates a protective cast around the curl while it dries, stabilizing the shape while hydrogen bonds reform and limiting how much the environment can disrupt them before they finish setting.
None of this changes your follicle biology, but it does give your curls the best possible conditions to do what they were built to do.
